Prior art switching architectures in digital communications networks typically employ data link (layer-2) services. ATM packet switching technology uses virtual connections for completing end to end communications through the ATM network. Virtual connection types include permanent virtual connections (PVC), switched virtual connection (SVC) or soft permanent virtual connection (SPVC). SVCs transport packets through the network and each packet contains routing and addressing information. These packets pass through the network sharing certain paths with packets from other messages. Permanent virtual circuits are ones in which terminals are permanently associated via a virtual circuit. An SPVC employs PVC type connections from the edge of the network to end users and SVC type switching within the network.
FIG. 1 shows an SPVC 12 that allows user traffic to flow between two ATM switches 14 and 16 through an ATM network 17, according to the prior art. The SPVC 12 has two endpoints 18 and 20 (each shown as a black dot in the figure) at the edges of the network. Each SPVC endpoint terminates on a port that provides direct connectivity to the CPE from their respective ATM switches. From the source node's perspective, (switch 14), the endpoint 18 is cross-connected 15 internally to the egress port 22 in which the SPVC 12 leaves the node. From the destination node's perspective (switch 16), the endpoint 20 is cross-connected 19 internally to the ingress port 24 in which the SPVC 12 call entered the node. The remainder of the SPVC 12 is shown as a dashed line through the ATM network cloud 17. SPVCs are setup between ATM switches using ATM signaling protocols such as the PNNI (private network-network interface) protocol.
FIG. 2 depicts an example DSL (digital subscriber line) application according to the prior art. In this example, an end user's computer 32 is connected via ATM switch 45, an ATM network 34, and associated equipment to three separate IP services. These separate services are network games provided by a game server 36, video on demand provided through an application server 38, and internet access provided through a broadband remote access server (BRAS) 40. A dedicated SPVC connection (SPVC1, SPVC2, and SPVC3) exists for each of these services. Each SPVC connection has an endpoint at the ingress port of a, DSL access multiplexer (DSLAM) 42 and another endpoint at an IP interface of a far-end ATM switch 50. In the far-end ATM switch 50, each SPVC has an internal cross-connect that connects its associated IP interface to an ingress port 52 of the switch. The user's computer 32 is connected to the DSLAM 42 via a CPE modem 43. For each SPVC, there is a PVC connection between the user's computer and an egress port on the CPE modem. Each corresponding SPVC and PVC pair share the same VPI/VCI (virtual path identifier/virtual circuit identifier) to make a connection between the CPE modem and the DSLAM.
FIG. 3 depicts a prior art SVC application that is substantially the same as that of FIG. 1, wherein a SPVC is used. The connection would originate from the CPE 70 connected to switch 72 and terminate on the ISP Server 74 connected to switch 76. The SVC 78 is shown as a dotted line through ATM network 80. Switches 72 and 76 have internal cross connects 73 and 77 respectively.
A problem with the prior art, particularly with regard to the example application shown in FIG. 2, is that it leads to a large number of PVC and SPVC connections. The PVC and SPVC resources have limitations; hence it is desirable to use these resources as efficiently as possible. In fact, experience has been that reaching PVC limitations in CPE modems has been a problem. Moreover, as the number of users and the services that they subscribe to grow to a very large number in such applications, the SPVC limitations in network nodes will become an issue. Furthermore, in the interest of setting up and maintaining connections, e.g. in response to network failures, it is desirable to minimize the total number of connections by using existing connections efficiently.
Another problem with the prior art as shown in FIG. 3 is that SVCs only provide connectivity to a single connection between CPE devices. If multiple services are required from different CPE equipment (possibly with different IP addresses) on the same node, then multiple SVCs are required from the source CPE, when a single SVC could suffice.